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Molecular Pathways Mediating Glial Responses During Wallerian Degeneration: a Dissertation

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Molecular Pathways Mediating Glial Responses During Wallerian Degeneration: a Dissertation University of Massachusetts Medical School eScholarship@UMMS GSBS Dissertations and Theses Graduate School of Biomedical Sciences 2015-05-14 Molecular Pathways Mediating Glial Responses during Wallerian Degeneration: A Dissertation Tsai-Yi Lu University of Massachusetts Medical School Let us know how access to this document benefits ou.y Follow this and additional works at: https://escholarship.umassmed.edu/gsbs_diss Part of the Molecular and Cellular Neuroscience Commons Repository Citation Lu T. (2015). Molecular Pathways Mediating Glial Responses during Wallerian Degeneration: A Dissertation. GSBS Dissertations and Theses. https://doi.org/10.13028/M26W2Q. Retrieved from https://escholarship.umassmed.edu/gsbs_diss/779 This material is brought to you by eScholarship@UMMS. It has been accepted for inclusion in GSBS Dissertations and Theses by an authorized administrator of eScholarship@UMMS. For more information, please contact [email protected]. MOLECULAR PATHWAYS MEDIATING GLIAL RESPONSES DURING WALLERIAN DEGENERATION A Dissertation Presented By Tsai-Yi Lu Submitted to the Faculty of the University of Massachusetts Graduate School of Biomedical Sciences, Worcester in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY May 14th, 2015 Interdisciplinary Graduate Program ii MOLECULAR PATHWAYS MEDIATING GLIAL RESPONSES DURING WALLERIAN DEGENERATION A Dissertation Presented By Tsai-Yi Lu The signatures of the Dissertation Defense Committee signify completion and approval as to style and content of the Dissertation _________________________________________________ Marc R. Freeman, Ph.D., Thesis Advisor _________________________________________________ Vivian Budnik, Ph.D., Member of Committee _________________________________________________ Carlos Lois, Ph.D., Member of Committee _________________________________________________ Neal Silverman, Ph.D., Member of Committee _________________________________________________ Yongjie Yang, Ph.D., Member of Committee The signature of the Chair of the Committee signifies that the written dissertation meets the requirements of the Dissertation Committee _________________________________________________ Eric H. Baehrecke, Ph.D., Chair of Committee The signature of the Dean of the Graduate School of Biomedical Sciences signifies that the student has met all graduation requirements of the school. _________________________________________________ Anthony Carruthers, Ph.D., Dean of the Graduate School of Biomedical Sciences Interdisciplinary Graduate Program May 14th, 2015 iii This work is dedicated to Juan Hsiao-Chi, for being my inspiration in the past several years, and to my family, for their unconditional support. iv Acknowledgements I would like to express my greatest appreciation to my advisor, Marc Freeman, for creating the best lab in the world and showing me how to be a great scientist. I would also like to offer my special thanks to my awesome mentor, Johnna Doherty, for patiently taking my questions from fly genetics to what a furry party would look like. My sincere thanks are also extended to all the past and present Freeman lab members, including Mary Logan, Jennifer MacDonald, Jennifer Ziegenfuss, Ozge Tasdemir-Yilmaz, Kimberly Kerr, Yuly Fuentes-Medel, Michelle Avery, Jeannette Osterloh, Allie Muthukamar, Edith Plada, Timothy Rooney, Zhiquo Ma, Lukas Neukomm, Thomas Burdett, Jaeda Coutinho-Budd, Owen Peters, Jemeen Sreedharan, Megan Corty, Jonathan Farley, Sukhee Cho, Lizzy Lewis, Yonca Kushkuly, Jack Wong, Gaynor Smith, Rachel Bradshaw, Tobias Stork, Nicki Fox Tapper, and Amy Sheehan, for giving valuable advice and making life in Worcester so colorful. I am forever grateful to be part of the UMMS GSBS family and would like to thank all the wonderful PhD mentors I met here, including Neal Silverman, Eric Baehrecke, Carlos Lois, Vivian Budnik, Claire Benard and Tony Ip. My special thanks also go to Yongjie Yang, for being my external committee member. Finally, I wish to thank the kindness of the Taiwanese community here at UMMS, especially Chun-Ting Chen, who passed away last summer, for being a respectful and truthful friend since my day 1 at UMMS, and Yung-Chi Huang, for always being on my side and reminding me why I started this journey in the beginning and how far I have come. v Abstract Glia are the understudied brain cells that perform many functions essential to maintain nervous system homeostasis and protect the brain from injury. If brain damage occurs, glia rapidly adopt the reactive state and elicit a series of cellular and molecular events known as reactive gliosis, the hallmark of many neurodegenerative diseases. However, the molecular pathways that trigger and regulate this process remain poorly defined. The fruit fly Drosophila melanogaster has glial cells that are strikingly similar to mammalian glia, and which also exhibit reactive responses after neuronal injury. By exploiting its powerful genetic toolbox, we are uniquely positioned to identify the genes that activate and execute glial responses to neuronal injury in vivo. In this dissertation, I use Wallerian degeneration in Drosophila as a model to characterize molecular pathways responsible for glia to recognize neural injury, become activated, and ultimately engulf and degrade axonal debris. I demonstrate a novel role for the GEF (guanine nucleotide exchange factors) complex DRK/DOS/SOS upstream of small GTPase Rac1 in glial engulfment activity and show that it acts redundantly with previously discovered Crk/Mbc/dCed-12 to execute glial activation after axotomy. In addition, I discovered an exciting new role for the TNF receptor associated factor 4 (TRAF4) in glial response to axon injury. I find that interfering with TRAF4 and the downstream kinase misshapen (msn) function results in impaired glial activation and engulfment of axonal debris. Unexpectedly, I find that TRAF4 physically associates with engulfment receptor Draper – making TRAF4 only second factor to bind directly to Draper – and show it is essential for Draper-dependent activation of downstream engulfment signaling, including vi transcriptional activation of engulfment genes via the JNK and STAT transcriptional cascades. All of these pathways are highly conserved from Drosophila to mammals and most are known to be expressed in mouse brain glia, suggesting functional conservation. My work should therefore serve as an excellent starting point for future investigations regarding their roles in glial activation/reactive gliosis in various pathological conditions of the mammalian central nervous system. vii Table of Contents Title ...................................................................................................................................... i Signature Page ................................................................................................................... ii Dedication ......................................................................................................................... iii Acknowledgements .......................................................................................................... iv Abstract .............................................................................................................................. v Table of Contents ............................................................................................................ vii List of Tables ..................................................................................................................... x List of Figures ................................................................................................................... xi List of Abbreviations ..................................................................................................... xiv CHAPTER I: Introduction .............................................................................................. 1 What are glia? What do they do? ............................................................................................ 2 Reactive gliosis, neural injury and clearance of cellular debris by glia .................................. 3 Glial responses during Wallerian degeneration in the CNS .................................................... 4 Drosophila as a model organism to study Wallerian degeneration ........................................ 6 Glial responses during Wallerian degeneration in the olfactory nerve injury model .............. 7 The diversity of glial cell types in Drosophila ........................................................................ 9 Draper-mediated glial engulfment of axonal debris .............................................................. 10 Activation of glial transcriptional responses by JNK and STAT after axon injury .............. 13 viii CHAPTER II: DRK/DOS/SOS Converge with Crk/Mbc/dCed-12 to activate Rac1 during Glial Engulfment of Axonal Debris .................................................................. 18 Introduction ............................................................................................................................. 19 Results ....................................................................................................................................... 21 DRK, DOS, and SOS are required for glial engulfment of axonal debris ............................ 21 Glial DRK is recruited to degenerating axons after injury .................................................... 23 DRK-SOS activation helps glia
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